Of course you're not personally responsible for bringing down Twitter, but if your computer isn't equipped with up-to-date anti-malware software and the latest version of your operating system, you could unwittingly be part of the problem.

Twitter has confirmed that its outage Thursday morning and subsequent intermittent problems were due to an ongoing denial-of-service attack. Facebook also "encountered network issues related to an apparent distributed denial-of-service attack, that resulted in degraded service for some users," according to a company spokesperson.

Typically a DoS attack, which is often called a distributed denial-of-service attack, results when multiple computers simultaneously try to access the site in question. Usually the reason that happens is because the attacking PCs are infected with malware that does the dirty work for whoever is behind the attack.

As Symantec blogger Marian Merritt pointed out, "It's often the case that DDoS attacks come from computers infected with bots, turning them into zombie computers doing their cybercriminal's bidding. "

You can help prevent your PC from being part of such an insidious scheme by:

* Using a good anti-malware suite from a reputable vendor such as Symantec, TrendMicro, McAfee, ZoneAlarm, or CA. You can find trial versions of such programs as well as the excellent AVG-Anti Virus Free Edition at CNET's Download.com

* Making sure your operating system has the latest patches. Visit Microsoft and Apple security pages for information.

* Avoid clicking on e-mail links that take you to Web sites you're not familiar with (malware is often distributed through "drive-by downloads" from unreputable or infected sites).

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About the author

Larry Magid is a technology journalist and an Internet safety advocate. He's been writing and speaking about Internet safety since he wrote Internet safety guide "Child Safety on the Information Highway" in 1994. He is co-director of ConnectSafely.org, founder of SafeKids.com and SafeTeens.com, and a board member of the National Center for Missing & Exploited Children. Larry's technology analysis and commentary can be heard on CBS News and CBS affiliates, and read on CBSNews.com. He also writes a personal-tech column for the San Jose Mercury News. You can e-mail Larry.
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